1. Field of the Invention
The present invention relates to electrical connectors, more particularly to electrical connectors with additional differential contact pair for transmitting high speed signals and with improved contact arrangement.
2. Description of Related Art
Personal computers (PC) are used in a variety of ways for providing input and output. Universal Serial Bus (USB) is a serial bus standard to the PC architecture with a focus on computer telephony interface, consumer and productivity applications. The design of USB is standardized by the USB Implementers Forum (USB-IF), an industry standard body incorporating leading companies from the computer and electronic industries. USB can connect peripherals such as mouse devices, keyboards, PDAs, gamepads and joysticks, scanners, digital cameras, printers, external storage, networking components, etc. For many devices such as scanners and digital cameras, USB has become the standard connection method.
As of 2006, the USB specification was at version 2.0 (with revisions). The USB 2.0 specification was released in April 2000 and was standardized by the USB-IF at the end of 2001. Previous notable releases of the specification were 0.9, 1.0, and 1.1. Equipment conforming to any version of the standard will also work with devices designed to any previous specification (known as: backward compatibility).
USB supports three data rates: 1) A Low Speed rate of up to 1.5 Mbit/s (187.5 KB/s) that is mostly used for Human Interface Devices (HID) such as keyboards, mice, and joysticks; 2) A Full Speed rate of up to 12 Mbit/s (1.5 MB/s); (Full Speed was the fastest rate before the USB 2.0 specification and many devices fall back to Full Speed. Full Speed devices divide the USB bandwidth between them in a first-come first-served basis and it is not uncommon to run out of bandwidth with several isochronous devices. All USB Hubs support Full Speed); 3) A Hi-Speed rate of up to 480 Mbit/s (60 MB/s). Though Hi-Speed devices are commonly referred to as “USB 2.0” and advertised as “up to 480 Mbit/s”, not all USB 2.0 devices are Hi-Speed. Hi-Speed devices typically only operate at half of the full theoretical (60 MB/s) data throughput rate. Most Hi-Speed USB devices typically operate at much slower speeds, often about 3 MB/s overall, sometimes up to 10-20 MB/s. A data transmission rate at 20 MB/s is sufficient for some but not all applications. However, under a circumstance transmitting an audio or video file, which is always up to hundreds MB, even to 1 or 2 GB, currently transmission rate of USB is not sufficient. As a consequence, faster serial-bus interfaces are being introduced to address different requirements. PCI Express, at 2.5 GB/s, and SATA, at 1.5 GB/s and 3.0 GB/s, are two examples of High-Speed serial bus interfaces.
From an electrical standpoint, the higher data transfer rates of the non-USB protocols discussed above are highly desirable for certain applications. However, these non-USB protocols are not used as broadly as USB protocols. Many portable devices are equipped with USB connectors other than these non-USB connectors. One important reason is that these non-USB connectors contain a greater number of signal pins than an existing USB connector and are physically larger as well. For example, while the PCI Express is useful for its higher possible data rates, a 26-pin connectors and wider card-like form factor limit the use of Express Cards. For another example, SATA uses two connectors, one 7-pin connector for signals and another 15-pin connector for power. Due to its clumsiness, SATA is more useful for internal storage expansion than for external peripherals.
FIGS. 49 and 50 show existing USB connectors. In FIG. 49, this USB connector 50 is an existing USB plug, male connector. In application, the USB plug 50 may be mounted on a board in the peripherals, or may be connected to wires of a cable 57 as shown in FIG. 49. Generally, an insulative outer housing 55 always be molded over a rear end of the USB plug 50 and the cable 57 to secure the USB plug 50, the cable 57 and the insulative outer housing 55 together. The USB plug 50 can also be mounted in an opening in a plastic case of a peripheral, like a portable memory device. The USB plug 50 represents a type-A 2.0 USB connector. The USB plug 50 includes an insulative plug tongue portion 52 formed of an insulating material, four conductive contacts 53 held on the insulative plug tongue portion 52 and an metal shell 54 enclosing the conductive contacts 53 and the insulative plug tongue portion 52. The metal shell 54 touches the insulative plug tongue portion 52 on three of the sides of the plug tongue portion 52 except a top side thereof. The conductive contacts 53 are supported on the top side of the plug tongue portion 52. A receiving cavity 56 is formed between the top side of the plug tongue portion 52 and a top face 541 of the metal shell 54 for receiving a corresponding insulative receptacle tongue portion 62 shown in FIG. 50. The conductive contacts 53 carry the USB signals generated or received by a controller chip in the peripherals.
USB signals typically include power, ground (GND), and serial differential data D+, D−. To facilitate discussion, the four conductive contacts 53 of the USB plug 50 are designated with numeral 531, 532, 533 and 534 in turn as shown in FIG. 49. In application, the four conductive contacts 531, 532, 533 and 534 are used to transfer power, D−, D+ and ground signals, respectively. The two central conductive contacts 532, 533 are used to transfer/receive data to/from the peripheral device or a host device. The four conductive contacts 531, 532, 533 and 534 can be formed of metal sheet in a manner being stamped out therefrom to four separated ones or formed as conductive pads on a printed circuit board (PCB, not shown) supported on the top side of the plug tongue portion 52.
FIG. 50 shows an existing USB receptacle 60, a female USB connector for mating with the existing USB plug 50. The USB receptacle 60 commonly is an integral part of a host or PC. The USB receptacle 60 also presents a type-A USB 2.0 connector. The USB receptacle 60 includes the insulative receptacle tongue portion 62 formed of an insulating material, four conductive contacts 63 held on the insulative receptacle tongue portion 62 and a metal shell 64 shielding the conductive contacts 63 and the insulative receptacle tongue portion 62. The conductive contacts 63 are supported on a bottom surface of the insulative receptacle tongue portion 62. Same to assignment of the four conductive contacts 53 of the USB plug 50, assignment of the four conductive contacts 63 of the USB receptacle 60 is contact 631 for power signal, contact 632 for D− signal, contact 633 for D+ signal and contact 634 for GND. Another receiving cavity 66 is formed between the bottom surface of the insulative receptacle tongue portion 62 and a bottom of the metal shell 64. In application, the USB plug 50 usually disposed in the peripheral device is inserted into the USB receptacle 60 mounted in the host or PC device. The plug tongue portion 52 is received in the receiving cavity 66 of the USB receptacle 60 and the receptacle tongue portion 62 is received in the receiving cavity 56 of the USB plug 50. After full insertion of the USB plug 50, the conductive contacts 531, 532, 533 and 534 of the USB plug 50 make a physical and electrical connection with the conductive contacts 631, 632, 633 and 634 of the USB receptacle 60, respectively, to transmit/receive signal to/from the host device to the peripheral device.
As discussed above, the existing USB connectors have a small size but low transmission rate, while other non-USB connectors (PCI Express, SATA, et al) have a high transmission rate but large size. Neither of them is desirable to implement modern high-speed, miniaturized electronic devices and peripherals. Thus, to provide a kind of connector with a high transmission rate for portability and high data transmitting efficiency, and with reasonable contact arrangement is much desirable.